[97] in Info-AFS_Redistribution
backup on rs_6k.
daemon@ATHENA.MIT.EDU (Kris Olander)
Wed Apr 3 16:23:57 1991
Date: Wed, 3 Apr 1991 16:02:11 -0500 (EST)
From: Kris Olander <kriso@northstar.dartmouth.edu>
Reply-To: kris.olander@dartmouth.edu
To: mb@transarc.com, info-afs@transarc.com
Cc: Kris Olander <kriso@northstar.dartmouth.edu>,
Marybeth,
Here are some results from our latest attempt at monthly
backups on the IBM RS 6000 8mm tape drive.
--------------
AllVolumes.mar.1: 487 vols, 882186 Kbytes
AllVolumes.mar.2: 442 vols, 921018 Kbytes
AllVolumes.mar.3: 143 vols, 1191196 Kbytes
--------------
The sizes listed above are the summation of sizes extracted from
a 'vos examine' command on each volume found on each of the
tapes; therefore, this is raw data.
Now, if we try to calculate what the actual amount of space
used on each tape by using the estimate of the 'end-of-record' (EOR)
size specified in /usr/afs/backup/tapeconfig, we'll get:
487*40K = 19480
882186+19480 = 901666 Kbytes total... for tape #1.
442*40K = 17680
921018+17680 = 938698 Kbytes total... for tape #2
143*40K = 5720
1191196+5720 = 1196916 Kbytes total... for tape #3
I am suspicious: 1) backup can't be using 40K to calculate
the tape size, because 901 Meg isn't even
close to the 1750 Meg I am using in tapeconfig,
2) fms on the 6k must be broken, the output:
fms test started
wrote 35215 blocks
Tape capacity is 576962560 bytes
File marks are 40030 bytes
3) I don't know how backup is watching for the
end-of-tape, but it appears to be faulty. If you
assume that each of the above tapes is using the
same EOR size, you should have,
(N1 * EOR) + S1 = (N2 *EOR) + S2
where N1 == number of volumes on tape1
N2 == " " " " tape2
S1 == sumation of sizes of all volumes on tape 1
S2 == " " " tape 2
EOR = (S2 - S1) / (N1 - N2)
1,2 EOR = ( 921018 - 882186 ) / ( 487 - 442 )
EOR = 862K
2,3 EOR = ( 1191196 - 921018 ) / ( 442 - 143 )
EOR = 903K
1,3 EOR = ( 1191196 - 882186 ) / ( 487 - 143 )
EOR = 898K
NOT 40 K!!! What's the point? Maybe someone
reading info-afs can answer that question.
Granted, the above equation is independant of the actual tape size.
Since I had 2 out of 3 tapes work fine, I'm going to drop the
/usr/afs/backup/tapeconfig tape size parameter down to 1650Meg.
This is a drop of 100Meg from its current value which is much
greater than any volume size we have on our cell, so I should
(cough, cough) be OK.
Is anyone out there using AFS 3.1 Backup?
-Kris
